|An ARB demo rig.|
The problem with a front locker is its effect on steering. The turning circle suddenly becomes huge. But it’s just a matter of knowing the vehicle and the characteristics of a locked front diff. However, the suppliers of lockers are understandably worried about liability issues. Sets of lockers are always wired so that the front one won’t work unless the rear one has been activated. That’s also the way it is on factory lockers, like those on the Land Cruiser 70 series, or on my Wrangler Rubicon. But if I were building a strictly off-road 4WD and could only afford one locker, it’d be on the front, for sure.
A visitor, A A Brown, left a comment that I've posted here rather than in the comments section because it provides a useful balance to the item above. He writes: "I have read what you have to say about front diff locks and I have to agree with the general thrust of the comment. However, a front locker can bite you badly if you're not quick with the 'off' switch. And it should never, ever be used on road or any high friction surface."